1. Field of the Invention
The present invention relates to a method of forming a coating on a quartz crucible for growing silicon crystal, the crucible comprising a devitrified layer, to prevent silicon oxide being mixed into raw material melt contained in the crucible in the manufacture of silicon crystals.
2. Description of the Related Art
In the Czochralski method for growing a single crystal, a crucible used to contain the raw material melt has a coating formed on the inner surface thereof to reduce mixing of impurities from the crucible to the raw material melt. The coating largely affects on the quality and yield of the single crystal and has been variously studied.
For example, JPH09-110579A discloses a method used in the Czochralski method for growing a single crystal, in which devitrification accelerator is attached to the inner surface of a crucible for containing the semiconductor material to be melted at a temperature of about 600° C. or less, and then the crucible is heated to a temperature above 600° C. to form a substantially devitrified silica layer on the inner surface. The devitrification accelerator includes those including alkali earth metal selected from the group consisting of calcium, barium, magnesium, strontium, and beryllium. By this method, while the Czochralski method is carried out, in particular, the polysilicon is melt, a stable seed crystal nucleus is formed in a nucleus formation region provided by the devitrification accelerator, glassy silica is crystallized on the crucible surface, and a substantially homogeneous and continuous devitrified shell of β-cristobalite is formed on the crucible surface. The substantially homogeneous and continuous devitrified shell (which corresponds to the devitrified coating in the present invention) formed on the inner surface of the crucible homogeneously dissolves when in contact with the molten raw material (silicon melt). The discharge of the β-cristobalite particles into the melt can thus be reduced, thereby minimizing the dislocation formed in the grown crystal. It is also advantageous that the devitrified shell formed on the crucible outer surface can strengthen the crucible.
Patent Literature 1: JPH09-110579A